Caseless smokeless powder pellet and method of preparing same



g- 26, 1969 J..W. SILVA ET AL 3,463,086

CASELESS SMOKBLESS POWDER PELIJET AND METHOD OF PREPARING SAME Filed Nov. 6, 1967 2 JOSEPH m SILVA EDWARD A. STABA ATTORNEY INVENTORSs United States Patent 3,463,086 CASELESS SMOKELESS POWDER PELLET AND METHOD OF PREPARING SAME Joseph W. Silva, New Haven, and Edward A. Staba, Higganum, Conn., assignors to Olin Mathieson Chemical Corporation, a corporation of Virginia Filed Nov. 6, 1967, Ser. No. 680,882 Int. Cl. F42]: 5/02, 9/02 US. Cl. 102-38 7 Claims ABSTRACT OF THE DISCLOSURE A caseless pellet comprising a propellant body of dry compacted fibrous smokeless powder and a slurry priming composition adhered to saidpropellant body.

This invention relates to a primed caseless pellet and the method of making said pellet. More particularly, the invention relates to the construction and method of manufacture of a pellet comprised of a body of fibrous smokeless powder grains formed into a predetermined configuration by a dry compacting process without the addition of binders, plasticizers and/0r solvents to adhere the grains together and primed with a water-based slurry priming composition.

Caseless ammunition of various types is well known in the art. Caseless ammunition has the advantage of eliminating the weight and cost of the conventional metallic case. The problems associated with caseless ammunition, including breakage and crumbling due to handling, moisture resistance, molding difliculty, and ignition reliability, have not been sufliciently overcome to allow known types of caseless ammunition to appreciably penetrate the conventional ammunition markets.

It is, therefore, an object of this invention to provide caseless ammunition which is economical to manufacture, can be readily and reliably ignited, has good handling properties, and can be molded into any desired configuration.

It is a further object of this invention to provide a readily ignited propellant mass which can be conveniently used as a source of power to drive a projectile such as a bullet, drive a piston, initiate ignition of other propellants or fuels or to do other useful work.

These and other objects and advantages of this invention will become more readily apparent from the detailed description and drawings below in which:

FIGURE 1 is an enlarged top-plan view of a caseless pellet formed in accordance with this invention;

FIGURE 2 is a cut-away side view of the pellet taken along the lines 22 of FIGURE 1.

There has developed a great impetus on the part of both the Government and private industry to develop molded structures'which would be suitable for use as a propellant for ammunition and the like. The advantages of eliminating the conventional metallic case to be rid of both the weight and cost of the case are well known. The advantages in simplification, weight reduction and cost of a weapon system which would not require the conventional ejection of a spent round have added greatly to the interest in caseless ammunition systems in recent times.

. It would appear that the prior art of forming caseless ammunition from smokeless powder granules has concerned itself largely with densely colloided smokeless. powder. As taught by R. L. Cook (US. Patent No. 3,092,- 525), previous dry molding methods employing colloided powders were unsuccessful because the molded powders thus prepared had little or no cohesion and crumbled readily. Recourse, therefore, was made to methods whereby the surfaces of smokeless powder grains were softened ice and cohesion was established by the melding of adjacent surfaces under pressure. Cook (US. Patent No. 3,092,- 525) teaches the use of plasticizer to obtain unitary structures; Andrews and Williams (US. Patent No. 3,037,417) teach the use of a volatile solvent contained in an aqueous medium; J. J. ONcil (US. Patent No. 2,988,436) teaches the use of a plastisol involving both nonvolatile plasticizer and a solvent for nitrocellulose.

The prior art described above may be characterized as wet processes and do not lend themselves to the easy handling, economy and molding versatility yielded by the dry process of the present invention.

The present invention relates to the use of grains of fibrous, shreddy types of smokeless powders, consolidated into unitary grains or shapes by the process of dry compaction. Such shapes are of particular advantage toward making caseless ammunition, primer cups and pellets for other power applications. Bulk smokeless powder is a material ideally suited for the purposes of this invention.

A basic understanding of certain aspects of the physical characteristics of bulk smokeless powder is helpful for a full understanding of this invention.

Bulk smokeless powder is today a relatively unknown and unused material, yet it was the first successful smokeless powder and dates back to 1864. Its history, characteristics and general method of manufacture are well described by Tenney L. Davis in Chemistry of Powder and Explosives, John Wiley, New York, 1941. Bulk powders are so named because for the same Weight, they have about the same bulk as black powder. In this, and in other pertinent characteristics, bulk powders difier radically from the dense colloided smokeless powder which is universally used in the ammunition of today.

Bulk powders consist always of nitrocellulose fibers which are stuck together but which are only very slightly or partially colloided. Bulk powders made by the processes described by Davis, op. cit., or modified as taught by A. S. ONeil in US Patent No. 1,608,808, or further modified for the various purposes of this invention, are always fibrous, shreddy, fuzzy or stringy structures as examined under magnification. Although the powder is in discrete, free-flowing grains, each grain is characterized by the aforesaid fibrous, stringy, shreddy or fuzzy structure.

It has been found that grains characterized by this fuzzy, shreddy, fibrous or stringy structure may be compacted in the dry state to form larger grains, charges, or shapes which faithfully retain the form into which they are compacted and whose combustion characteristics may be varied as taught in this disclosure. In practice, the dry, free-flowing characteristic of these powders permit them to be used in the type of equipment commonly employed to mold articles from metallic powders and to be molded into any form which can presently be secured from powder metallurgy.

In accordance with this invention, a pellet 1, shown in FIGURE 1, comprises a cylindrical body portion 2. The cylindrical body portion 2 may be formed by the compaction of bulk powder or other fibrous smokeless powder in a press into the desired configuration. As mentioned above, the fibrous characteristic of the free-flowing grains of bulk smokeless powder allow the grains to interlock and form a strong cohesive mechanical bond. Body portion 2 is formed with a central cavity 3 to receive a sensitive priming composition 4 which will cause deflagration of the pellet when the priming mix is ignited. A water-base slurry priming composition has been found to be ideally suitable for purposes of this invention and will be described in detail below. The priming cavity 3 is preferably formed with sloping sidewalls 5, and a relatively fiat bottom. This configuration has been found to give the best distribution of the priming composition in the primer cavity. The pellet 1 may be utilized as a source of power to drive projectiles, bolts, studs, nails, etc. It may be used as a power capsule to start a small gasoline engine or the like or as a means of igniting a larger propellant mass. One of the major contemplated uses of a pellet of this type, however, would be as a propellant for ammunition. In this use, the pellet 1 would be attached to the rear portion of a bullet 6, as shown in dotted lines in FIGURE 2. The pellet may be attached to the bullet 6 by mechanical means, by adhesives or in a number of other ways which will readily occur to those skilled in the art.

The dry compacted pellet ll, shown in the drawings, when formed from bulk smokeless powder, can have a various number of characteristics imparted to it. The compacting pressure used to form the pellet can be varied from a pressure of about 3,500 p.s.i. to as high as 75,000 p.s.i. This would permit the compacted structure formed to have a density varying from as low as about 0.85 gram per cubic centimeter to as high as about 1.45 grams per cubic centimeter. With the true density of nitrocellulose being about 1.6, it will be readily understood that pellet structures can selectively be formed with porosity ranging from about 50 percent to about 10 percent. The porosity of the formed pellet has a direct effect upon the burning rate of the pellet.

Further, it has been found that dry compacted bulk smokeless powder acts as a binder to hold, in a firm structure, solid, granular modifiers which may be added to change the ignition or combustion characteristics of the propellant. Firm structures have been made and fired with the solid modifiers enumerated below. All modifiers were of fine particle size and all of which were added to the bulk smokeless powder simply by a conventional dry blending operation. They were added in amounts ranging from 1 percent to 25 percent by weight of the bulk smokeless powder. The modifiers evaluated by firing included: graphite, potassium nitrate, potassium dichromate, potassium sulfate, lead chromate, strontium peroxide, barium peroxide, nitroguanidine, aminotetrazole, PETN, TNT, RDX, red phosphorous, nitroaminoguanidine and nitrostarch. The dry compacted bulk smokeless powder acts as a binder not only for modifiers as above, but also for densely colloided propellant granules which otherwise could not be made coherent in a dry compaction process. The versatility with which the fibrous compacted powder of this invention can be modified allows it to be used in applications ranging from primer cups to caseless propellant ammunition.

With the problem of forming a preformed pellet overcome in accordance with this invention, as described above, there still remains the problem of priming the pellet so that it can be ignited reliably under normal as well as adverse conditions. The problems encountered in priming a preformed pellet in accordance with conventional techniques is described in detail below, along with a detailed description of the preferred primer and priming techniques employed with this invention.

In the fabrication of a pellet, as shown in FIGURE 2 and described above, it is essential to avoid inclusion of any metallic or non-combustible plastic components other than the projectile or bullet where the contemplated application of the pellet is as a round of caseless ammunition. Thus, it is inadvisable to apply a conventional primer having metallic cup and anvil components as a means of ignition of the caseless cartridge. If this were done, the metallic cup and anvil components, left as residue after firing, could enter the breech mechanism when the breech is opened, and cause jamming thereof. Altemately, there is also the possibility that such metallic primer com ponents might come to rest in the bore after a caseless cartridge is fired, and dangerously obstruct the passage of a succeeding projectile. For these reasons, priming for the ignition of a caseless cartridge, such as seen in FIG- URE 2, is applied directly to the briquetted propellant mass, within a cavity 3 molded into the end of the briquette facing breechward so the priming may be acted upon by a conventional firing pin or other means housed in a tool or weapon.

If the usual metallic primer cup is excluded from the caseless cartridge, for the reasons cited above, problems are encountered in the application of priming to the cartridge. Conventional priming mixtures consist of crystalline or granular ingredients having particle sizes generally in the range of 45 microns to microns. Typically existing priming mixtures used in both military and commercial small arms ammunition throughout the world are comprised of the following ingredients:

Lead Styphnate PETN (pentaerithritoltetranitrate) Barium nitrate or lead nitrate Antimony sulfide or ground glass Aluminum Calcium Silicide Tetrazene In conventional practice, such mixtures are prepared and charged in a dry condition or in a water-moistened condition wherein water comprises generally 8 to 20% of the weight of the composition. Mixtures of either the dry type or the moist type are disbursed from the bulk condition into charges required for individual primers by manually filling or charging holes or cavities within a charge plate, and transferring the unit charges therefrom into the usual metallic primer cup. The weight of the unit priming charges is governed by the volume of the holes in the charge plate. After the priming charges are transferred to the primer cups, the unit charges are pressed within the cup so they conform to cup contour, and become firmly implanted therein. In the dry priming process, no adhesive or bonding material is normally present in the priming mixture to aid in bonding the granular ingredients into a durable pellet, but bonding and implantation are achieved by application of high pressure to the punches used in the pressing operation. Typically, pressures applied range from about 500 to about 5,000 pounds per square inch of punch area. In

the moist priming process, a water soluble gum or binder is generally included in the mixture to aid in bonding the granular ingredients into a durable pellet, which, together with the greater fluidity of the priming charge afforded 'by the moist condition, permits achievement of an adequate degree of bonding and implantation at substantially reduced punch pressure compared to pressure applied in the dry priming process. Typically, pressures applied in the wet priming process range from about'50 to 500 pounds per square inch of punch area. In both the dry and moist priming process, the pressure applied to the priming mass reduces the porosity thereof, generally in proportion to the magnitude of the pressure applied. Such reduction in porosity is generally considered to enhance percussion sensitivity. Although the pressure applied in the moist priming process is substantially lower than that of the dry process, the pressing operation cannot be omitted without seriously jeopardizing primer reliability. Applying such pressures to a compacted mass of propellant will invariably result in some breakage and waste.

If one seeks to apply existing priming mixtures to caseless cartridges by existing techniques, a number of serious problems arise. In the transfer of priming charges from the charge plate to the metallic primer cups of the conventional priming process, it is necessary to orient the cups, mouth uppermost, and in a holding plate having the same number of holes and holes spacing as the charge plate. Since the briquetted propellant charge may correspond to chamber diameter, particularly if it furnishes structural support for the chambered cartridge, the diameter of the briquetted mass would be much greater than that of the metallic primer used in conventional cased .ammunition, and the number of units that could be obtained from charge plates and holding plates of reasonable size would be reduced significantly. In addi tion, fabrication of the holding plate for the briquetted propellant charge would be more diflicult and expensive than fabrication of holding plates for metallic primer cups because the simple configuration and small size of the latter. Such cost differentials are significant because they would nullify the potential cost advantage of the caseless system.

If the conventional priming process were followed, after transfer of the priming charge to the cavity of the briquetted propellant mass was accomplished, the next step in the process would involve pressing the priming charge to bond the granular particles and implant the mass of priming firmly in the cavity. While this process step is readily accomplished without encumbrance in pressing priming into metallic primer cups, pressing priming into cavities in briquetted propellant masses presents serious problems. In addition to the difiiculty of fabricating a suitable holding plate to properly support and orient the briquetted masses, to achieve alignment with the pressing punch, the friable character of the briquetted propellant is such that weakening or fracture of the mass can result on application of pressure. While it is possible with typical nitrocellulose propellants of either the single or double base type, to briquette the granular material into exceedingly durable masses by solvent bonding of the particles and/or high molding pressures, excessive strength is disadvantageous. In order to attain a suitable burning rate, and duplicate the ballistic performance of a similar propellant charge in the granular state, it is. essential to have the briquetted mass in a porous and friable condition so that fracture of the mass into suitably small fragments will occur on impact of the firing pin or by virtue of the brisance of the priming. Thus, the operation of pressing priming into briquetted propellant masses must be done with care, and even then, scrap losses due to breakage appear inevitable.

If, instead of conventional priming mixtures, a slurry priming is utilized in priming briquetted propellant masses for the caseless system, not only are the problems described above eliminated, but a greatly simplified process results. Further, this form of priming may readily be charged by automated mechanical means instead of the manual method required for conventional priming mixtures. Explanation of how these advantages arise may be more readily advanced if the properties of the slurry priming found most useful with this invention are first described in detail. The term slurry priming is used to describe a mixture consisting of solid priming ingredients in a finely divided state suspended in a fluid medium, and having such fluidity that it may be dispensed and metered by techniques normally applied to fluids. Priming of this type could be regarded as being similar to paint, wherein the particles of explosive and other priming ingredients, taken collectively, could be regarded as the pigment, and the fluid medium as the vehicle. The dimensions of the solid particles are much smaller than those of solid ingredients of conventional priming mixtures, and they approach or equal dimensions of typical pigment particles. The small particle size permits preparation of a fairly stable suspension, having a uniform composition, and avoids rapid settling of the solid particles out of the vehicle. To be useful in the priming art, it is essential that such priming have a high concentration of solids so that a suitably high charge of priming may be obtained from a relatively small volume of slurry. Typically, primer cups have a small volume, and similarly the volume of the cavity that can be formed in a briquette propellant mass is limited. Accordingly, it is essential for the slurry to have a high content of solid particles and yet possess suflicient fluidity so that it may be dispensed by techniques generally applied to liquids. Further, it is essential that the slurry be stable with respect to its rheological properties, over a reasonably prolonged period, so that it may be dispensed in a reproducible manner by mechanical means, and yield a uniform charge of priming in the finished ammunition component.

In order to fulfill these rather exacting requirements, it is essential to choose solid chemical materials having suitable physical properties. Significant physical characteristics include specific gravity, solubility (in the fluid), appropriate particle size and particle shape, etc. Obviously, it is also essential that these materials comprise a functionally acceptable priming mixture having suitable percussion sensitivity, propellant ignition effect, stability, etc. In addition, it is also desirable to provide priming that is sufiiciently brisant to cause or assist in causing fracture and disintegration of the briquetted propellant as required to promote a suitable burning rate. It is also desirable to have priming which does not produce a large amount of clinging solid residue which might foul the chamber, the bolt face, or the firing pin conduit.

Examples of slurry priming mixtures which substan tially fulfill all the requirements elicited above are as follows:

Particle Size Range Maximum Particle Useful Dimension, Percentage Materials (microns) Range Stabanate 1 (low apparent density). 2-15 5-100 1-60 0-10 l-60 0-15 pigment 1-15 0-15 Nitroaminoguanidin l-60 0-50 Karaya gum s 1-5 Gum Arabic 1-10 1 The proprietary name applied to the double lead salt of styplniic acid0 and nitroarninotetrazole, which is the subject of U.S. Patent No. 3 31 569.

2 Pentaerythritoltetranitrite.

Examples of specific formulations are are follows:

Application of the slurry priming described above to briquetted propellant is readily achieved by the dip-pin technique, wherein a rod of suitable diameter to yield the desired charge weight of priming is dipped in the slurry to such a depth that on removal a pendant drop collects at the lower end of the vertically positioned rod. The charged rod is then moved so the pendant drop comes in contact with the bottom of the cavity in the briquetted mass of propellant, whereupon the drop is deposited within the cavity and flows to conform with the profile of the cavity. Alternately, it is possible to deposit a drop of slurry on the item to be charged by means of metering pump or cam operated injector. By either technique, it is possible to conduct the charging operation automatically by feeding the uncharged units in a properly oriented manner to a mechanically operated charging station.

Part of the water in the drop of slurry priming migrates into the surfaces of the cavity in the briquetted propellant described above due to the porosity of the mass and consequent capillary action. As the gums present are dispersed in this water, gum is carried into the surface of the briquetted mass. On subsequent evaporation of Water drawn into the briquetted mass by capillary action, the gums present are deposited in the dry state and provide a bonding effect. As water is removed from the drop of slurry, both by migration into the propellant mass and by evaporation during the drying operation which follows charging, the mass of priming shrinks as water 7 is removed, so that the dry mass is remarkably free of voids. The net result on drying is a well-implanted prim: ing mass, which has low porosity and exhibits good percussion sensitivity.

In summation, slurry priming needs only to be applied as a drop to the priming cavity of a caseless cartridge, as described above, and then dried to remove Water. No subsequent pressing operation is required to achieve implantation, or reduce porosity of the priming mass. The resultant structure is an economical, dependable and readily ignitable pellet which can be used in any number of applications to supply useful power.

The advantages of a dry compacted and slurry primed pellet as described above with respect to ease of manufacture, economy, reliability, handling properties, etc., will be readily understood and appreciated by those skilled in the art.

While this invention has been described in detail with respect to a preferred embodiment shown in the drawings, it is contemplated that this invention covers all variations and modifications which are included within the spirit and scope of the appended claims.

We claim:

1. A primed caseless pellet comprising a fibrous smokeless powder molded in the dry state into a predetermined configuration and a measured amount of a dried slurry priming composition adhered to said configuration.

2. The pellet of claim 1 in which said slurry priming composition includes from 5 to 100% of the double lead salt of styphnic acid and nitroaminotetrazole.

3. A primed pellet comprising dry compacted fibrous grains of nitrocellulose interlocked under pressure to form a unitary cohesive structure, a primer cavity formed in said structure and a readily ignitable dried slurry priming composition positioned in and adhered to said cavity.

4. The pellet of claim 2 in which said configuration includes ignition or combustion modifiers which comprise 5. A caseless ammunition pellet of dry compacted bulk' powder formed to a predetermined configuration, said configuration having a depression formed in one face thereof operative to receive a primer and a dried slurry primer composition deposited in said cavity and adhered to said configuration.

6. A method of forming a caseless primed pellet comprising the steps of:

(a) measuring a predetermined amount of a propellant comprised substantially of discrete grains of nitrocellulose having a fibrous character;

(b) forming said propellant by pressure into a pellet of predetermined configuration having a primer cavity;

(c) metering a predetermined amount of a fluid priming composition into said primer cavity; and

(d) drying said pellet to provide a unitary structure readily ignitable by conventional means.

7. Caseless ammunition including a porous propellant body formed substantially of fibrous nitrocellulose grains dry compacted into a unitary structure, a bullet adhered to one end of said propellant body and a dried slurry. priming composition adhered to an opposite end of said propellant body by the penetration of a portion of said priming composition into said porous propellant body.

References Cited UNITED STATES PATENTS 3,320,887 5/1967 Quinlan et a1. 102-45 3,372,643 3/1968 Kvavle 10299 CARL D. QUARFORTH, Primary Examiner S. J. LECHERT, Assistant Examiner US. Cl. X.R. 

